The basic telephone numbering plan administration system (“NPA”) used universally in telephony today, whether for conventional wireline or wireless service, is based on geographical assignment. Generally, wireline and wireless mobile communication systems operate subscriber terminal units with unique directory numbers that are geographically associated to one home switch within the carrier's network and these switches and directory numbers are assigned on a geographical basis determined by the subscriber's home or business physical location. In this configuration, call delivery between systems is performed through static call translations, routing and service databases that route the terminating call to the home switch associated with the subscriber unit.
In other words, when a call is made to a subscriber unit's telephone number, the call is delivered by a carrier to a switch assigned to serve the subscriber's unit. Upon receipt of the call from the carrier, the home serving switch associated with that telephone number will execute a query to an appropriate Service Control Point (SCP), which is a system that includes a database, to obtain special routing instructions. Information contained within the SCP database is used by the switching system to route the call within the terminating carrier's network, including between switching and over inter-switch transport, to the subscriber's unit (for example, in wireline telephony, when the subscriber has invoked a call-forwarding service to another termination point).
For wireless subscribers, in response to this query, the SCP will then query the associated mobile service provider terminal location register (Home or Visitor Location Register HLR/VLR) by using industry standard IS-41 Location Request messaging. Upon request, the mobile switching system will poll the mobile terminal unit to determine the availability and location of the mobile terminal unit. Once determined, the mobile system replies to the SCP query with a Location.sub.—Request return signal to report the mobile terminal unit's status. If the mobile unit is available, the mobile system returns the mobile's identification number to the SCP for call delivery routing to the identified mobile terminal unit. If the mobile user is not in the serving area of the home switch associated with the called telephone number, the wireless carrier must utilize valuable internal network routing resources, including switch capacity and transport between switches, to route the call to the appropriate switch presently serving the terminating unit. If the mobile system replies to the SCP query indicating that the mobile terminal unit is unavailable, the switching system will direct the terminating call delivery to the home switch serving the subscriber's unit for proper treatment (e.g., announcement, voice mail, or other treatment).
Voice-over-Internet-Protocol (VoIP) calls present another variation in call handling and promise a much higher degree of personal mobility. Whether wireless or wired, the subscriber unit does not necessarily have a “directory number” permanently associated with the unit. Instead, when a subscriber connects to the Internet the user indicates that he/she is available at a particular address. For example, using the up and coming internet standard Session Initiation Protocol (SIP) for call setup, modification and teardown, when a user first connects to the network a SIP REGISTER request is sent to a Registrar database that maps the directory number (and the user's associated IP address) with the current physical (layer 2) network address of the subscriber's SIP device. In this way, calls can be routed to either the user's office, home or mobile SIP-phone, whichever is the current location of the user. Alternatively, using the older H.323 architecture and H.225 signaling, gatekeeper(s) perform a similar function, providing a translation service between real IP addresses and aliases.
While both known systems have been successful in providing terminating call delivery to subscriber units, the results are less than satisfactory. Inefficiencies in these call delivery techniques have resulted in wasted capital resources, increased operating expenses, and latent call delivery rates due to unnecessary internal call routing within the terminating carrier's network. This is particularly true in cases where (say) a GSM mobile phone is roaming in a foreign country or in the VoIP case (actually promoted/encouraged by VoIP providers), where the home directory number has been allocated from the numbers assigned to a foreign country, to provide a sort of super Foreign Exchange (FX) service. In addition, call completion and service quality can be negatively impacted by unnecessarily routing calls through multiple switches and over inter-switch transport. Much of this inefficient internal routing could be eliminated or sharply reduced if the calls were simply terminated to the switch presently serving the subscriber unit, versus the switch associated with the called telephone number. Therefore, a need exist for a system and method for dynamically determining, before handing a call off to the terminating carrier, the switch presently serving the called subscriber's unit and terminating calls to that switch versus terminating calls merely based on the switch associated with the terminating telephone number.